It often takes an outsider to look inside. This is especially true of the United States, where self-scrutiny has never been a habit, and where "anti-American" is almost as bad as terms of abuse can get. Let me say, upfront and centre, that Gary Younge loves America. He would agree, I think, with Emerson, who wrote that "America is a poem in our eyes". But Younge's poem is no panegyric. It's a bemused but surreal epic.

One could hardly find a better guide than Younge, who will go anywhere at the drop of a 10-gallon hat, always unafraid to say exactly what he thinks. He's also wise, arguing that journalists should be fair and honest, yet aware that "the idea that they can be objective is nothing less than insidious". He suggests that one must get beyond the bare facts, and proves his point in these various dispatches, which gather under four broad headings: war, race, politics, and culture.

Younge is aware of his own good luck in having the US as his subject during "one of the most difficult and crucial eras in its recent history". He arrived in New York City as a correspondent for this paper only a week after September 11, when the US "enjoyed the support of the full range of global opinion". Already Younge could sense the temporary status of this bonhomie. A great thirst for revenge could be felt in American streets, and - in the cowboy hands of the Bush league - there was little hope that anything good lay ahead.

None the less, one could hardly have guessed that America and its blood brothers would soon attack a sovereign state that had nothing to do with September 11, and that they would do so under false pretences. That illegal and unprovoked attack would soon lead to tens of thousands of deaths, "diverting our attention and resources from the very people we should be fighting - al-Qaida". Younge puts the blame squarely on the shoulders of Bush and Blair, who still refuse to bear the responsibility for this catastrophe, which has far-reaching moral and political implications, most of them dire.

On race, Younge writes as a black Briton: something most Americans can hardly imagine as a category. When he first meets someone, he usually encounters a mixture of "bemusement, amazement, and curiosity". He has to allow them a few moments to compose themselves. One white woman in Louisiana, for example, gasped: "I had no idea," in a tone that Younge's grandmother might have used had he come out as a cross-dresser.

Always a keen-eyed portraitist, Younge profiles several black American icons, such as Jesse Jackson and Maya Angelou, both of whom combine monstrous egos with an aggressive will-to-power. In these cases, "I shall overcome" seems to have replaced by "We shall overcome." But they are both obsessive workers. Indeed, Jackson "calls newspaper editors in the middle of the night, records interviews with radio stations before his colleagues are awake, and usually seeks advice from a self-selected court of academics, activists and commentators around the country before his first meeting of the day". Angelou tours the vast expanse of America like a rock star in her mega-bus, which comes "complete with a double bed, spare rooms, shower, cooking facilities and satellite television". The ironies of all this are not lost on Younge.

In fact, Younge delights in ironies. In the lively section of essays on politics, he charts the rise of the right, the demise of the left. But he does so with full attention to the shifting ground beneath his feet. It's never simple in the US, and he knows it. In "Left Over?" - a brilliant critique of the American left and its struggle to survive - he quotes George Packer to the effect that the Democratic party has no foreign policy whatsoever: "They can't stand up because they have nowhere to stand, no alternative vision of what purpose America's enormous power in the world should serve." With typical energy, Younge interviews a wide range of important figures on the left: Noam Chomsky, Howard Zinn, Katha Pollitt. "It's a testament to the left's strength," he writes, "that from the bleakest of scenarios they have created a space within [which] they are not just existing, but expanding. It is a sign of their weakness that they are expanding from such a small base that they are able to influence public opinion but not lead it."

Some of the most memorable moments in this collection are small ones, as when Younge pays a visit to the parents of Jonathan Kephart from Venango County, in western Pennsylvania, the first soldier from to die in combat since the Vietnam war. This is Deerhunter country, and Kephart's father is a born-again Christian who works for a lumber company. He spends much of his time trying to convert Younge, who listens to the bereaved parent with palpable sympathy but horror as well. What Kephart's father says about God's will in Iraq is nothing less than terrifying, however, and Younge knows he need add nothing by way of comment: "God has a plan for the ages ... Bush will hold back the evil a little bit."

This epic vision of the "Disunited" States is both frightening and encouraging. Anyone should tremble before the rare combination of arrogance and ignorance found everywhere in America the Beautiful, from the prairies to the mountains white with snow (as the song goes) but especially in the current White House.

But there is much to admire there, too: the wild energy, the mix of races and notions, and the sheer intensity of the culture, which Younge tracks from Hollywood to Harlem with a cool eye but obviously warm heart.

· Jay Parini's The Art of Subtraction: New and Selected Poems is published by George Braziller